1. Field of the Invention
This invention relates to extra fine particle size cobalt metal powder and to a method for obtaining such powder from an impure cobalt source, and more particularly relates to obtaining such powder by reducing a black precipitate obtained from the digestion of a cobalt pentammine chloride solution.
2. Prior Art
It is known to separate cobalt from nickel by a process which includes forming pentammine sulfate complexes of the two ions in solution. German Pat. No. 2,319,703. However, it has been found that soluble cobalt ammine sulfates can only be reduced while still in solution, under pressure, and with the aid of catalysts. Furthermore, the resulting cobalt powder is not fine particle size. Finally minor impurities, below about 2 weight percent, cannot be removed by recrystallization of the cobalt ammine sulfates. Thus, more complex methods of removing such minor impurities, must be employed.
U.S. Pat. No. 3,928,530, issued Dec. 23, 1975 to Bakker et al, and assigned to International Nickel Co., teaches a process for the separation of nickel and cobalt by forming pentammine chloride complexes in solution containing a high concentration of ammonium chloride, and precipitating cobalt pentammine chloride at a basic pH. Such a system, however, is not suitable for the separation of cobalt from cationic impurities such as iron, manganese, copper, etc. since such impurities would also precipitate out at the basic pH.
In German Pat. No. 1,583,864, cobalt is recovered from scrap by digestion of the scrap in HCl and MgCl.sub.2 solution, followed by removal of Fe and Cr impurities by precipitation at a moderately acid pH (2-4), followed by extracting a cobalt chloride complex with a long chain tertiary ammine in an aromatic solvent. Cobalt chloride is then stripped from the extractant and may be converted to cobalt metal by converting to cobalt oxide or cobalt hydroxide and then reducing to cobalt, e.g., by hydrogen reduction.
While the above process enables removal of undesired cationic impurities such as Fe and Cr, it nevertheless requires the use of organic extractants and solvents, and necessitates employing a stripping step to separate the extracted cobalt from the organic phase.